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created or modified since the last lower-level backup A dump level of 1 will back up only files that have changed since the last level 0 backup The dump level 2, in turn, will back up only files that have changed since the last level 1 backup (or 0 if there is no level 1), and so on up to dump level 9 You can run an initial complete backup at dump level 0 to back up your entire system and then run incremental backups at certain later dates, backing up only the changes since the full backup Using dump levels, you can devise certain strategies for backing up a file system It is important to keep in mind that an incremental backup is run on changes from the last lower-level backup For example, if the last backup was 6 and the next backup was 8, then the level 8 will back up everything from the level 6 backup The sequence of the backups is important If there were three backups with levels 3, then 6, and then 5, the level 5 backup would take everything from the level 3 backup, not stopping at level 6 Level 3 is the nextlower-level backup for level 5, in this case This can make for some complex incremental backup strategies For example, if you want each succeeding incremental backup to include all the changes from the preceding incremental backups, you can run the backups in descending dump level order Given a backup sequence of 7, 6, and 5, with 0 as the initial full backup, 6 would include all the changes to 7, because its next lower level is 0 Then 5 would include all the changes for 7 and 6, also because its next lower level is 0, making all the changes since the level 0 full backup A simpler way to implement this is to make the incremental levels all the same Given an initial level of 0, and then two backups both with level 1, the last level 1 would include all the changes from the backup with level 0, since level 0 is the next lower level not the previous level 1 backup

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Recording Backups

Backups are recorded in the /etc/dumpdates file This file will list all the previous backups, specifying the file system they were performed on, the dates they were performed, and the dump level used You can use this information to restore files from a specified backup Recall that the /etc/fstab file records the dump level as well as the recommended backup frequency for each file system With the -W option, dump will analyze both the /etc/dumpdates and /etc/fstab files to determine which file systems need to be backed up The dump command with the -w option just uses /etc/fstab to report the file systems ready for backup

Operations with dump

The dump command takes as its arguments the dump level, the device it is storing the backup on, and the device name of the file system that is being backed up If the storage medium (such as a tape) is too small to accommodate the backup, dump will pause and let you insert another dump supports backups on multiple volumes The u option will record the backup in the /etc/dumpdates file In the following example, an entire backup (dump level 0) is performed on the file system on the /dev/hda3 hard disk partition The backup is stored on a tape device, /dev/tape

dump -0u -f /dev/tape /dev/hda5

NOTE You can use the mt command to control your tape device; mt has options to rewind, erase,

and position the tape The rmt command controls a remote tape device

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Backup Management

The storage device can be another hard disk partition, but it is usually a tape device When you installed your system, your system most likely detected the device and set up /dev/tape as a link to it (just as it did with your CD-ROMs) If the link was not set up, you have to create it yourself or use the device name directly Tape devices can have different device names, depending on the model or interface SCSI tape devices are labeled with the prefix st, with a number attached for the particular device: st0 is the first SCSI tape device To use it in the dump command, just specify its name